III-nitride materials include gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN) and their respective alloys (e.g., AlGaN, InGaN, AlInGaN and AlInN). In particular, gallium nitride materials include gallium nitride (GaN) and its alloys such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN). These materials are semiconductor compounds that have a relatively wide, direct bandgap which permits highly energetic electronic transitions to occur. Such electronic transitions can result in gallium nitride materials having a number of attractive properties including the ability to efficiently emit blue light, the ability to transmit signals at high frequency, and others.
In many applications, III-nitride materials are typically grown heteroepitaxially on a substrate. However, property differences between III-nitride materials (e.g., gallium nitride materials) and many substrate materials can present challenges. For example, gallium nitride materials (e.g., GaN) have a different thermal expansion coefficient (i.e., thermal expansion rate) and lattice constant than many substrate materials and, in particular, silicon. These differences may lead to formation of cracks and/or other types of defects in gallium nitride material layers that are grown heteroepitaxially on silicon. In some methods, a transition layer is used to mitigate the effects of these differences in order to grow high quality gallium nitride material on silicon. However, these differences (and others) have limited the performance and commercialization of structures and devices that include gallium nitride material formed on silicon substrates.
III-nitride materials (e.g., gallium nitride materials) are being investigated in high frequency (e.g., RF and power management) device applications. When energy is dissipated in high frequency devices through undesirable mechanisms (e.g., parasitic losses and capacitive coupling), the performance of the device may be impaired. These so-called parasitic losses can reduce output power, switching speed, power gain, and efficiency. Therefore, it is generally desirable to limit the parasitic losses in high frequency (and other types of) RF and power management devices.